U.S. Pat. No. 5,244,380 describes a premix burner of the type of a partial cone burner, of which the combustion chamber, which axialwards conically widens, is bounded on the radial side by two partial cone shells which are arranged in a position with one inside the other in such a way that their partial cone center axes extend with an offset in relation to each other, wherein the partial cone shells mutually overlap along their partial cone shell side edges and enclose with each other tangentially extending air inlet slots through which air can enter the swirl chamber for further mixing through with fuel. For fuel feed, the premix burner, which is described in the aforesaid publication, provides a fuel nozzle which is installed centrally inside the burner, which fuel nozzle at least partially leads axialwards into the burner from sides of the combustion chamber in the region of the smallest diameter of the combustion chamber, and provides at least one fuel nozzle through which liquid fuel is feedable in the form of a fuel spray cloud which conically expands in the swirl chamber.
The process of the liquid fuel feed and also the subsequent combustion process is basically dividable into the following phases which are temporally separable from each other:
1. Atomizing of the liquid fuel by means of a fuel atomizing nozzle,
2. Vaporizing of the liquid fuel droplets which form in the course of the atomization process,
3. Forming of a fuel-air mixture and, finally,
4. Igniting and combusting of the fuel-air mixture.
In the event that the duration in which the first three phases take place is shorter than the dwell time of the fuel inside the burner (Phase 4), it is to be assumed that the combustion process takes place with complete premixing and with low release of nitrogen oxides. On the other hand, if the dwell time of the fuel inside the combustion chamber is constantly smaller than the time span inside which the rest of the fuel feed phases are forming, then the combustion takes place in the course of a diffusion, as result of which ultimately high portions of nitrogen oxide are released and, furthermore, high turbine exhaust temperatures occur. In order to reliably avoid this, the liquid fuel emerging through the central fuel nozzle is mixed with demineralized water, by means of which are reduced the emission of nitrogen oxide and also the high burner exit temperatures, through which ultimately also the service life of the burner components and also the components which come into contact with the hot gases is limited.
In order to optimize the fuel distribution forming inside the burner and to create preconditions under which it can be ensured that a burning off of the fuel which is fed to the burner is as complete as possible, the premix burner which is described in the aforementioned patent document provides additional fuel nozzles which are installed in the region of the air inlet slots. In this case, the atomization of the liquid fuel takes place in the direction of the longitudinal extent of the respective air inlet slots in order to enable a mixing through of the fuel with the inlet air just before entry into the combustion chamber. However, the only small penetration capability of the fuel feed in the longitudinal direction to the air inlet slots is disadvantageous. This can result in the inner wall regions of the partial cone shells being able to be wetted with fuel, as a result of which burn-off phenomena occurring directly on the inner walls allows the risk of local material overheating happening on the partial cone shells themselves.